1. Field of the Invention
This invention relates to a technique for improving the resolution of a successive comparison type AD conversion method.
2. Description of the Background Art
Improvement of the resolution of an AD conversion method requires high-precision tuning of the configuration of a ladder resistor and an analog circuit inside an AD converter to be used. However, for an improved resolution by one bit, for example, a voltage value by resistors division to be taken out at the ladder resistor may double, which requires a corresponding increase in the number of resistors included in the ladder resistor. This results in such a problem of an increase in footprint of the AD converter on an IC chip.
Japanese Patent Application Laid-Open No. 10-107632 (1998) discloses an exemplary AD conversion method with an improved resolution by switching between a fine comparator and a coarse comparator connected to a ladder resistor.
An AD converter used in the AD conversion method disclosed in the above publication includes two kinds of devices (comparator and encoder) for fineness and coarseness. This results in a problem of a corresponding increase in footprint.